A self-driving Uber car struck and killed a pedestrian early Monday morning in Tempe, Arizona, marking the first pedestrian fatality of the self-driving car era in the United States.

The woman, 49-year-old Elaine Herzberg, died at the hospital of her injuries. The vehicle was in autonomous mode, Tempe police told a local ABC affiliate, and an operator—capable of taking control of the car at any moment—was behind the wheel. “Our hearts go out to the victim’s family,” Uber said in a statement. “We are fully cooperating with local authorities in their investigation of this incident.” The company is also pausing driverless car operations in Phoenix and elsewhere.

Arizona has established itself as a testing ground for Uber and Google’s Waymo, each of which has deployed fleets of autonomous vehicles on the streets of the Phoenix metro. Sunny days and reliable car-centric infrastructure make the area well-suited for the evolving technology, which struggles with unusual road and weather conditions.

More importantly, Arizona has leveraged its reputation as a regulation-free, disruption-friendly state. Waymo has been testing self-driving cars in the Phoenix metro since last spring, including cars without assisting drivers since November—a move that few states allow. Quartz reported last month that Waymo was given a license in January to operate a taxi service in Arizona and hoped to have a commercial self-driving service on the market by the end of 2018. Uber, meanwhile, had deployed self-driving trucks in Arizona earlier this month. Just this month Arizona Gov. Doug Ducey drafted the state’s first set of rules for autonomous vehicles.

Monday’s incident will be a test for how much citizens are willing to tolerate AV experimentation on public roads. So far, there has been little public pushback as politicians and regulators race to welcome the AV industry. But there have been only a few notable accidents. In July 2016, a driver using Tesla autopilot died when his car drove into the back of a tractor-trailer. A self-driving Uber ran a red light in San Francisco just hours after the company first deployed the technology there.

You can expect that Uber, local regulators, and tech evangelists will make much of the Tempe police report that the woman was outside a crosswalk, although North Mill Avenue—the eight-lane road the victim was attempting to cross—has only one crosswalk in nearly two miles of road, making jaywalking a requirement of the urban design. (Jaywalking arrests and pedestrian fatalities are also disproportionately concentrated in communities of color.)

The crash will bolster street safety advocates’ case that regulators and companies are putting people at risk by experimenting on city streets. One of the central arguments for self-driving cars in the long term is that they will be safer than human drivers. In the short term, Google has gone to great lengths to reassure the public that the technology is safe, funding a project called “Let’s Talk Self-Driving” in collaboration with the National Safety Council, Mothers Against Drunk Driving, and other road safety advocates. The Uber crash could jeopardize that narrative.

Update, March 19, 2018: The photo on this post was changed to match the make of the Uber car involved in the accident.